As the development of nanoscale mechanical, electrical, chemical and biological devices and systems increases, new processes and materials are needed to fabricate nanoscale devices and components. Making electrical contacts to conductive lines has become a significant challenge as the dimensions of semiconductor features shrink to sizes that are not easily accessible by conventional lithography. Optical lithographic processing methods have difficulty fabricating structures and features at the sub-60 nanometer level. The use of self assembling diblock copolymers presents another route to patterning at nanoscale dimensions. Diblock copolymer films spontaneously assemble into periodic structures by microphase separation of the constituent polymer blocks after annealing, for example by thermal annealing above the glass transition temperature of the polymer or by solvent annealing, forming ordered domains at nanometer-scale dimensions.
The film morphology, including the size and shape of the microphase-separated domains, can be controlled by the molecular weight and volume fraction of the AB blocks of a diblock copolymer to produce lamellar, cylindrical, or spherical morphologies, among others. For example, for volume fractions at ratios greater than about 80:20 of the two blocks (AB) of a diblock polymer, a block copolymer film will microphase separate and self-assemble into a periodic spherical domains with spheres of polymer B surrounded by a matrix of polymer A. For ratios of the two blocks between about 60:40 and 80:20, the diblock copolymer assembles into a periodic hexagonal close-packed or honeycomb array of cylinders of polymer B within a matrix of polymer A. For ratios between about 50:50 and 60:40, lamellar domains or alternating stripes of the blocks are formed. Domain size typically ranges from 5-50 nm.
A lamellar-phase block copolymer material has been used for making line features on a substrate. However cylinders self-assemble more rapidly and corrects defects faster than lamellae. Researchers have reported producing lines of upward-facing, half-cylinders of a minority block of a block copolymer in a matrix of the majority block through self-assembly of a cylindrical-phase morphology block copolymer on a chemically neutral surface. After removal of the matrix material, the half-cylinders form a masking structure over the underlying substrate. However, subsequent etching tends to undercut and isotropically etch the matrix material that remains under the half-cylinder lines, which will negatively affect etch resolution of the substrate. Applications for forming structures in an underlying substrate for semiconductor systems require a complex layout of elements for forming contacts, conductive lines and/or other elements such as DRAM capacitors.
It would be useful to provide methods of fabricating films of line arrays of ordered nanostructures that overcome these problems.